When a man experiences the pains of the gout, he is conscious of them; in other words, he feels interiorly, that it has produced very marked, very distinct changes in him, without his perceiving, that he has received an impulse from any exterior cause; nevertheless, if he will recur to the true source of these changes, he will find that they have been wholly produced by exterior agents: they have been the consequence, either of his temperament; of the organization received from his parents; of the aliments with which his frame has been nourished; besides a thousand trivial, inappreciable causes, which congregating themselves by degrees produce in him the gouty humour; the effect of which is to make him feel in an acute and very lively manner. The pain of the gout engenders in his brain an idea, so modifies it that it acquires the faculty of representing to itself, of reiterating as it were, this pain when even he shall be no longer tormented with the gout: his brain, by a series of motion interiorly excited, is again placed in a state analogous to that in which it was when he really experienced this pain: but if he had never felt it, he would never have been in a capacity to form to himself any just idea of its excruciating torments. The visible organs of man's body, by the intervention of which his brain is modified, take the name of _senses_. The various modifications which his brain receives by the aid of these senses, assumes a variety of names. _Sensation_, _perception_, and _idea_, are terms that designate nothing more than the changes produced in this interior organ, in consequence of impressions made on the exterior organs by bodies acting on them: these changes considered by themselves, are called _sensations_; they adopt the term _perception_ when the brain is warned of their presence; _ideas_ is that state of them in which the brain is able to ascribe them to the objects by which they have been produced. Every _sensation_, then, is nothing more than the shock given to the organs, every _perception_ is this shock propagated to the brain; every _idea_ is the image of the object to which the sensation and the perception is to be ascribed. From whence it will be seen, that if the senses be not moved, there can neither be sensations, perceptions, nor ideas: this will be proved to those, who can yet permit themselves to doubt so demonstrable and striking a truth.